Hydrocarbon conversion



Patented Mar. 13, 1945 HrnnocARBoN CONVERSION- Harrison C.

Mayland, Chicago,

lll., assignor l to UniversalOil Products Company, Chicago, lll., a acorporation of Delaware Application September 19, 1941,` Serial No.411,448

3 Claims.

This invention relates to a process for the catalytic cracking of ahydrocarbon oil for the production of high octane number gasolinewherein the activity of the catalyst gradually decreases during theprocessing cycle due to the deposition of deleterious carbonaceousmaterials on the catalyst surfaces and wherein the activity of thecatalyst is restored by the periodic regeneration of the catalyst by thecombustion of the carbonaceous materials with hot oxygen containinggases, `More specifically, this invention is concerned with catalyticcracking processof the type described above which also-includes therecycling` of the insufficiently converted hydrocarbons back to thecatalytic mass.

One of the main diillculties encountered in most of the presentcatalytic operations lies in the fact that the reflux condensate formedin the` operation is refractory and is not readily susceptible tofurther catalytic treatment. If this reflux condensate is admixed withthe fresh feed and recycled back to the catalyst zone, the conversionper pass through the catalyst zone greatly decreases, This decrease inconversion per pass makes it necessary to operate using high recycleratios which not only decreases the plant capacity considerably but alsoincreases the repumping and reheating requirements to produce thedesired quantity of gasoline.

Increasing the severity aiding in decreasing the tional disadvantages inthat greater amounts. of light gases and catalyst deposit are formed.This additional catalyst deposit; increases the capacity of theregenerating equipment necessary, thereby considerably increasing Toavoid the diilculties recited above,V it has beenvproposed to conduct ona once-'through basis wherein only the fresh v feed is charged to thecatalyst and the refractory reflux condensate is cracked in a thermaloperation. method of conducting the operation would, of course, have theadvantage-of eliminating the difficulties attending the recycling of ahighly refractory reflux condensate back to the catalyst mass but it toov.tagesfv 1'-, l

" Y It is known that in the catalytic cracking op-4 eration, a gasolineis produced which has a high antiknock value, usually between 8 and 12octane recycle ratio has addiof the processing While,

the catalytic operation of aparticular reflux the -cost of theoperation. v

Y absolute boiling point in degrees Rankine divided carbon oil thecharacterization has definite disadvan- 'Y Anumbers higher than theantiknock value of gasolines produced thermally. g g a given amount oi'oil, ablejto Therefore,v when it is more desirgreater proportion of theoil to obtain a greatercproportion of a for the same quantity tivitydecreases during the processing cycle due to deposition of carbonaceousmaterials on the catalyst surface which, of course, results in adecrease in the conversion per pass, there is a correspondingdecrease/in the refractoriness of the reflux condensate formed. Thisrefractoriness decreases fairly rapidly during the processing cycle andit was found that thereflux condensate produced during the major part ofthe processing cycle was susceptible to further catalytic treatment. Thepresent invention discloses a process wherein the reiiux condensateproduced during a Particular portion of the process period which hasattained a denite degree of susceptibility to further catalytic crackingis recycled back to the catalyst. Evidences have been found which seemto indicate that there is a relationship existing between theparaiiinicity of the reflux condensate and its susceptibilitytocatalytic cracking. Experimental tests have shown that the more paramnicthe.

reflux condensate is the greater its susceptibility to catalyticcracking. The relative paramnicity condensate is obtained by thedetermination of which will provide a. simple method formaintaining andcontrolling the operation at an optimum recycle ratio.'I'hischaracterization factor is an indication of the relativeparalnicity of a hydrocarbon oil. When dealing with a pure hydrocarbonthis factor is dened as a cube root of its by the specific gravity at F.However, when dealing with complex mixtures suchas a. hydrofactor of theoil may be dened as the cube 4 average boiling pointin degrees Rankinedivided by the specific gravity at 60 plete chemical analysis isavailable the cubic average boiling point maybe calculated as a'cube ofa sum of the product ofthe times the cube root of the boiling point ofeach component -expressed in degrees Rankine. Il' a c' complete analysisisnot available the -cubic avby-a, correlation of the volume averageboiling pointvand:

its characterization factor root of its cubic F. When a comvolumefraction the Engler distillation y .catalyst used, but it .tion factorreferred to above does value of this factor.

curve slope. When this ratio is of the order of 12 or more, the stock ispredominantly parafllnic, and as thecharacterization factordecreases theparafflnicity of the hydrocarbon oil also decreases,

As has been previously stated, the feature of this invention lies in therecycling of that portion of the reflux condensate which has attained adefinite degree of susceptibility to further catalytic cracking asdetermined by its characterization factor. By recycling this portion ofthe reflux condensate having the parafnnicity, the optimum quantity ofthe charglng stock can be catalytically cracked without introducing the-difficulties attending the use of a high recycle ratio in a totalrecycle operation.

The optimum portion of the reflux condensate will, of course, vary withthe charging stock and has found that it is usually possible to maintainthe most eiilcientl catalytic cracking operation if the characterizationfactor of thev redux condensate recycled back to the catalyticconversion zone is of the order of about 11 or-higher.

It must be understood that this characterizanot mean the average factorbut refers to the instantaneous For instance, during the operation, thevalue of the characterization factor of the reiiux condensate formedgradually increases. When this factor reaches about 1l this material isrecycled back to the catalyst zone.

desired degree of The material formed in the early part of the cyclehaving a lower characterization factor is either sent to storage orcharged to some other process such as a thermal cracking process.

In one specic embodiment the present invention discloses a catalyticcracking process which comprises contacting a hydrocarbon oil undercracking conditions of temperature and pressure with a cracking catalystdisposed in a reaction zone, withdrawing the reaction products,fractionating said products and separating the gasoline boiling rangematerials from the insuficiently converted hydrocarbons, and recyclingback to the catalyst, that part of the insuiiiciently convertedhydrocarbons which has attained a desited degree of parainicity.

The invention will be more fully understood by the description of theaccompanying drawing which illustrates in conventional side elevationone form ci' apparatus in which the objects of the invention can beaccomplished.

Referring to the drawing, the charging stock which may comprise, forexample, a Mid-Continent gas oil, is introduced through line lcontaining valve 2 into pump 3 which discharges through valve c and isthereafter commingled with insuinciently converted hydrocarbons formedas hereinafter set forth.- The resulting mixture passes through line 5'iitoheating coil 6 disposed in furnace 1. The resulting 'mixture isheated to the desired temperature and'leavesrheating coll 6disposediniurnace vl and is conducted through line 8 containing 'valve 9into reactor l0 wherein it is contacted y tha catalyticl mass atsuitable conditions 'for the production of lower boiling rangehydrocarbons. The temperature in reactor l0 may range from 70D-1200o F.and preferably from SOO-1000* F., vand the pressure mayY range fromsubstantially;atmospheric,to 200 pounds or moreper square inch.

' Reactor l0 may comprise, for example, a con- 'verslo'n zone .of thekheat exchanger the'catalystfiscontained in a plurality of elontypewherein Y generation.

' line l1 or'lS depending upon the catalytic operation,

gated tubular elements of relatively small diameter, provisions beingmade for passing some suitable heat convective fiuid such asfcombustiongases in indirect heat exchange relationship with said tubular elementsto supply heat to the reactants during conversion and to cool thecatalyst and regenerating gases during regeneration. Reactor Hl, on theother hand, may comprise a cylindrlcal vessel containing one or aplurality of beds of catalytic material, said vessel being insulated toreduce the radiation losses therefrom, so that conversion reaction maybe accomplished substantially adiabatically.

The catalyst disposed in reactor i0 may coinprise, for example, powder,pellets, or granules containing synthetically prepared, purified silica,or other siliceous and refractory materials composited with one or moreof the compounds selected from the group consisting of alumina,zirconia, and thoria. In addition, the hydrosilicates of alumina, acidtreated clays, or the like, have also been found to be effective in thecracking treatment of hydrocarbon vapors. Although the catalysts aboverecited are generally considered to be the preferred catalysts, theiruse is not to be construed as a limiting feature, for various othercatalysts Well-known to those in the art may be employed within thebroad scope of the invention.

During` the catalytic cracking of hydrocarbon oils, considerable amountsof carbonaceous materials deposit on the catalyst surfaces therebydecreasing the activity of the catalyst. Itis necessary, therefore, toperiodically regenerate' the catalyst by the combustion oi thecarbonaceous materials with hot oxygen containing gases. It isdesirable, therefore, in order that the operation may l be carried outas a continuous process to employ at least two reactors so that whilethe catalytic material in one reactor is being used for processing thehydrocarbon reactants, the catalytic material in the other reactor maybe undergoing re The invention disclosed lherein is particularlyadaptable to a system using more than two reactors in which theprocessing period is staggered, as will be more fully explained later inthis specicatlon.

i The reaction products leaving chamber l@ are conducted through line Ilcontaining valve i2 into iractionator i3 which is operated atsubstantially the same or at a reduced pressure in reference to reactorit. In fractionator i3, the gasoline boiling range hydrocarbons areseparated from the higher boiling hydrocarbons and the former materialsare withdrawn through line li containing valve I5 and may be thereaftercooled, condensed, and separated from the light gases by any of the Wellknown methods of stabilization.

The higher boiling `materials are withdrawn through line I6' characterof the materials. During the first'part of the processing period inreactor ID, the insulciently converted hydrocarbons separated out infractionator I3, will possess a low degree of paraftlniclty and will notbe very susceptible to further catalytic cracking. Therefore, duringthis part of the processing cycle,-the insufficiently convertedhydrocarbons will be withdrawn through line IB' into line I'l containingvalve I8 and sent to storage. These materials may be cracked, if sodesired, in a non thereby augmenting the total yield of gasolineobtained from a given quantity of the charging stock.

As the processing cycle continues. the catalyst and may be conductedinto either I the y circulation of. only that portion of theinsufactivity decreases due to depom'tion of carbonaceous material onits surface. of the reflux condensate formed gradually increases until areflux condensate having the desired characterization factor is formed.It is apparent that the desired characterization factor will varydepending upon. the catalyst and the charging stock being used butordinarily the desired reflux condensate will have a characterizationfactor of the order of about 11 or higher. Therefore, when thecharacterization factor of the higher boiling materials separated out infractionator i3 reaches the desired predetermined value, valve I8 isclosed and are conducted through line i9 containing valve 20 intoreservoir 2i.` The recycle oil is withdrawn from the reservoir throughline 22 containing valve. 23 in pump 24 which discharges through valve25 into line 28. 'I'he hydrocarbons conducted through line 26 are mixedwith the fresh feed entering through valve and the mixture is sent toheating coil5. The recycle 4ratio is proportioned so that a constantrate of recycle oil and fresh feed may be maintained, thereby permittingthe constant firing of furnace 1 without the introduction of anyadditional heating problems.

The invention disclosed herein is also adaptable to many other methodsof operation. For example, a, multiple reactor system may be used inwhich the processing cycle is staggered, perhaps with a lag ofone-quarter cycles between reactors. By the introduction of a secondfractionating step, it would be possible to recycle the higher boilinghydrocarbons from the reaction zone which is farther advanced in theprocessing cycle to the reaction zone just starting the processingcycle,l thereby conducting the same type of cracking operation asdescribed previously in this specification.

The following examples will presentthe distinct the hydrocarbons Theparamnicity advantages obtained when using the process disclosed herein.drawing and the following examples are not intended to place any unduelimitations on the present invention since there are many modifications.

which will fall under its broad scope.

pressure of 30 pounds per square inch gauge and at a liquid hourlycharge rate corresponding to a space velocity of 1 with a composite'catalyst com- --prising silica, alumina, and zirconia for a two hourprocessing period. During the operation a porreilux condensate formed isbeing continually withdrawn and sent to storage. The remaining portionof reflux condensate is sent back' to the reaction zone. 'Ihe averagecharacterization factor of the withdrawn about 11.5. I'he yields are39.0% gasoline, 9.1% gas, 2.5% catalyst coke, bottoms.

Thefsame oil is charged to the catalyst under stime processingconditions butwith the reand 49.5% fractionatorv The precedingdescription of the fing gasoline boiling range flciently convertedhydrocarbons, withdrawing carbons formed during the iiciently convertedhydrocarbons having a characterization factor of Il or higher. The vmorerefractory materials having a characterization factor below 11 which areformed during the early portion of the processing cycle are withdrawn tostorage. When the characterization factor of the reflux condensatewithdrawn from the fractionator reaches about il, this material 'isrecycled back to the reaction zone. kThe resulting yields are 7% gas,41.7% gasoline, 1.8% catalyst coke, and 49.5% fractionator bottoms.'I'he withdrawn fractionator ottoms have an average characterizationfactor of 10.7.

The utility of the present invention is shown by the preceding examples.When using the process' disclosed herein, `the gasoline yield isincreased approximately 7%, the 'gas yield ltiecreased approximately 22%and the catalyst coke is decreased approximately 28%.

I claim as my invention:

1. A process for the conversion of hydrocarbon oil which comprisessubjecting said hydrocarbon oil to contact under suitable processingconditions with a cracking catalyst disposed within a reaction zone,separating the gasoline boiling range materials from the insuiiicientlyconverted hydrocarbons, withdrawing insufficiently convertedhydrocarbons formed during the early portion of the processing periodhaving a characterization factor below about 11, and recycling theinsumciently converted hydrocarbons formed during the second portion ofthe lproce period having a characterization factor in excess of about 11back to the reaction zone.

\ 2. A process for `the conversion of hydrocarbonoil which comprisessubjecting said hydrocarbon oil to contact at a temperature within therange of about 700 to l20 F. with a c catalystl disposed within areaction zone, separating gasoline boiling range materials frominsufciently converted hydrocarbons, withdrawing insufficientlyconverted during the early portion' of the processing period having acharacterization factor below about il,

and recycling insufficiently converted hydrocarbons formed during theysecond portion of the processing period having a characterization fac'-tor of at least 11 back to the reaction rone.

3.' A process for the conversion of a hydrocarbon oil which comprisessubjecting said hydrocarbon oil to-contact at a range of about '100to1200 F. and under a pres.

sure of atmospheric toy about 2M vpounds per* square inchsuperatmospheric with a cracking catalyst disposed within a reactionzone, separan materials from insufinsumciently converted hydrocarbons-formed during the early portion of the processing,- riod having acharacterization factor below about i1, and recycling insumcientlyconverted hydroi second portion ofthe processing period having a tionfactor of at least ll "back to lone.

HARRIBO, accumulano` hydrocarbons formed temperature within the

